What is my zebra plant suffering from

Cut this leave off and trow away, it contains a pest.

Over and or under watering— or bouts of not enough and then too much

Also don't be afraid to prune those bad leaves it will help it.

Alocasia zebrina also commonly called giraffe neck, wild alocasia, and zebra elephant ear. Prefers 5.5-6.5 PH. Water in frequent small amounts to prevent root rot. Good drainage soil. Prefers indirect sun can tolerate full shade but will not bloom in shade. Also prefers alot of humidity. Does not like alot of fertilizer.

Overwatering or too many nutes. Ive got a similar indoor plant that does this when ever I water too often or if I give it nutes more often than a few times a year. For a tropical plant they sure are fussy on their waterings. Or too bright a light does it too in summer if near a warm window.